This invention relates to the production of fluid catalytic cracking catalysts. These fluid catalytic cracking catalysts (hereinafter "FCC catalysts") are generally prepared from a mixture of zeolite particles, clay, an alumina-containing binder, and a silica source. These constituents are admixed in an aqueous slurry in certain proportions, then the aqueous slurry is subjected to drying to form the essentially water-free FCC catalyst particles.
The productivity of the process is generally limited by the solids content of the aqueous slurry subjected to the drying step. The higher the solids content of the slurry, the better the throughput rate in a given piece of equipment with simultaneous better utilization of the heat input in the dryer. When the drying operation is accomplished by using conventionally available drying equipment, such as spray-driers, the viscosity of the aqueous slurry plays a significant role. Spray driers are usually equipped with nozzles or rotating discs and if the slurry has a high viscosity, which is related to the solids content of the slurry, plugging of the nozzles or stoppage of the discs will occur interrupting the production of the FCC catalysts. Consequently, a balance must be found between the desired production rate and the solids content of the aqueous slurry.
In our copending application Ser. No. 420,439, filed Sept. 20, 1982 now U.S. Pat. No. 4,443,553, a process for reducing the viscosity of aqueous slurries containing the FCC catalyst forming constituents, is described. The reduction in viscosity and corresponding improvement in the production rate is achieved by the incorporation of an additive having the general formula of (Al.sub.2 (OH).sub.6-y Cl.sub.y).sub.x where x=1 to 6 and y=1 to 2. This additive is incorporated in the aqueous slurry in an amount equivalent to from about 0.5 to about 2.5% by weight calculated as Al.sub.2 O.sub.3 and based on the solids content of the slurry. The addition of this additive to the slurry allows a significant increase in the solids content of the slurry, for example, up to about 20% by weight.
Although the addition of the (Al.sub.2 (OH).sub.6-y Cl.sub.y).sub.x additive provides significantly improved production efficiency and energy savings, the FCC catalyst particles produced will contain a small quantity of chloride residue. Although in most catalytic cracking applications, the residual chloride content (0.1-0.3% by wt.) of the FCC catalyst does not create problems, there are a few processes where the presence of the chloride could interfere with the efficiency of the catalytic cracking. Consequently, there has arisen a need to find an additive which on the one hand reduces the viscosity of the aqueous slurry and on the other hand does not leave behind an anionic impurity which could interfere with any FCC operation. It has been surprisingly discovered that there is an alumina-containing additive, having the general formula of Al.sub.2 (OH).sub.5 NO.sub.3, which accomplished the desired viscosity reduction, but when incorporated in the aqueous slurry used for the FCC catalyst preparation, will not provide any residual effect in terms of catalyst performance and/or activity.